An embodiment of the present invention relates to x-ray imaging systems. In particular, an embodiment of the present invention relates to multiple plane imaging in digital x-ray systems using the servo-tomo function.
Today, doctors and technicians commonly have access to very sophisticated medical diagnostic x-ray imaging devices. Typically, during the operation of an x-ray imaging device, an x-ray source emits x-ray photons under very controlled circumstances. The x-ray photons travel through a region of interest (ROI) of a patient under examination and impinge upon a detector. In the past, x-ray imaging devices employed film based or CR plate detectors. However, recent developments have led to solid state detectors comprised of a grid of discrete detector elements that individually respond to exposure by x-ray photons. One such detector is described in U.S. Pat. No. 4,996,413 to McDaniel et al. Regardless of the detector used, however, the goal remains the same, namely to produce a clear resultant image of the desired structures of interest within the ROI.
There is an inherent difficulty associated with producing a clear resultant image, however. In particular, because the x-ray photons travel through the entire patient, the image formed on the detector is a superposition of all of the anatomic structures through which x-ray photons pass, including the desired structures of interest. The superposition of anatomic structures is sometimes referred to as “anatomic noise”. The effect of anatomic noise on the resultant image is to produce clutter, shadowing, and other obscuring effects that render the resultant image much less intelligible than the ideal clear resultant image.
One technique commonly utilized to produce a clear resultant image of the anatomy of interest is tomography. Tomography blurs the structure both above and below a tomographic plane that contains the desired structures of interest by moving both the x-ray tube and the detector during a single exposure. Several methods may be used to produce a tomographic image. Each method utilizes several parameters to identify the tomographic plane which must be specified by the x-ray technician. In linear tomography, the x-ray tube and the detector maintain the same relationship to each other. The x-ray tube and the detector may be mechanically fixed so that their relationship remains constant, or the x-ray tube and the detector may maintain a constant relationship by utilizing angulation to keep the x-ray tube aimed at the detector.
Another technique used by x-ray imaging devices involves a “servo-tomo” function. Systems operated in accordance with a servo-tomo function do not mechanically fix or maintain the same relationship between the x-ray tube and the detector. Instead, the servo-tomo function controls movement of the x-ray tube and the detector relative to one another, but such movement is not identical. The servo-tomo function allows the x-ray tube and the detector to move in opposite directions, similar to linear tomography, but also to move at different speeds and distances. Thus, the x-ray tube may move a larger distance at a faster speed compared to the distance and speed of the detector during the x-ray exposure. The servo-tomo function may be used to view anatomy such as joints and the liver, for example.
Typically, one tomographic plane of the anatomy of interest is not sufficient for medical diagnosis. Often a radiologist desires to see multiple tomographic planes, with each tomographic image focused on a different point in the patient's anatomy. The acquisition of successive tomographic planes is called multi-plane tomography.
Several disadvantages exist with the current use of multi-plane tomography. For example, for x-ray systems that utilize the servo-tomo function with a film based or CR plate detector (i.e. analog systems), the film or CR plate may need to be replaced with another film cassette or CR plate before additional tomographic images can be acquired. Also, the radiologist must wait for the images to be developed before evaluating the images. Additionally, one or more parameters used to define the tomographic plane need to be modified by the x-ray technician before the next tomographic image can be acquired. The foregoing steps result in increased time for the examination, thus resulting in a lower patient throughput and a lower utilization rate of the x-ray machine. The examination time may further increase if, once the film or CR plates are developed, it is determined that additional or different slice information is desired. It is also possible that unnecessary exposures may be taken because the images are not reviewed as they are acquired. Thus, a need has long existed in the industry for a method and apparatus for multi-plane acquisition that addresses the problems noted above and previously experienced.